Wednesday, October 6, 2010

1971 CB350 Cafe

The next project in the shop is rebuilding a 1971 CB350 into a true biz cafe racer for a customer.  We agreed on a look for the bike, and the work began.  The first thing I did was to build a stainless 2-1 exhaust while I had the bike together.  The bike was in fairly rough shape when purchased, though the body work looked alright, the tires were flat, shocks were mush and tank was full of kreem covered rust!

I got the bike up on a stand and waited until I had some time to work on it, then I stripped everything off that wasn't going to be part of the completed bike or wasn't in good enough shape to keep.

Before doing any body work, I decided it might be a good idea to go through the engine and do a thorough reconditioning, along with replacing any parts that were worn past service limits.  Pulling the engine was very easy, once I removed the mounting bolts, the motor lifted right out of the frame.  

The engine turned out to be pretty rough too.  When we changed the oil after getting the bike, we cleaned a mess of metal shavings and chips from the oil filter (not a good sign).  Assuming it was probably a chewed up tensioner, we hoped for the best.  Turns out the engine was chewing itself to bits and the previous owner probably thrashed the hell out of this bike.  Going through the top end, I discovered the cam was badly pitted on the lobes, the rocker arms were also ground down due to the pitted cam, the cam chain was stretched probably because of the added friction, the tensioner was indeed chewed to bits.  When I got the head off, the condition was less bad, the valve seats looked serviceable, though one of the exhaust valves was too pitted to get a cup on for lapping.  
One of the combustion chambers also showed some damage from what might have been a foreign object, but the valve seats weren't impacted, so the piston and head could still be used.  Looking at the cylinders, I thought they were serviceable, until I did a hone and discovered some deep scoring that will require at least a .25mm overbore and piston kit to match.  

Cleaning up the parts was pretty simple, and facing the mating surfaces will ensure a good seal and proper reassembly.  Once replacement parts are approved by the customer, rebuilding can proceed.  The good news is basic inspection of the bottom end showed splitting the cases will probably not be necessary.  And my advice is to replace the cam chain with a heavy duty type with a rivet master link so the chain can be upgraded without splitting the crankcase and involving that much more work.  

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